Let's see,

HK quality is superb
Their guns eat everything
Extremely reliable
They last a very long time
Lightweight
Accuracy is consistent
Good recoil management
Excellent ergonomics with swappable side panels and backstraps. Three sets of each size come with each gun
High capacity
Trigger/Safety variants to fit nearly all tastes
Good sights
Good enough for many military and police agencies across the world.

That should do it.